Sometimes a photograph taken with a digital camera is blurred. One reason for this is camera shake. When taking a photograph with a camera held in one's hands, if the camera is not held sufficiently steady, the resulting image will be blurred. Of course, camera shake may be prevented by holding the camera stationary, but the length of time one must hold the camera steady varies, depending on the shutter speed used. In low light conditions longer exposure periods are needed to produce an image that is not too dark and, for this reason, the camera must be held stationary for relatively long periods under such conditions.
During the period when the photographer is viewing the scene and preparing to take a shot, he may at times hold the camera sufficiently steady to capture a shake-free image, while at other times he may not hold the camera steady enough. Different individuals have different abilities to hold a camera steady and a particular individual's ability may vary from time to time. In addition, the camera must be held steady for different periods, depending on light conditions. For these reasons, it can be difficult for the photographer to know when he is keeping the camera sufficiently stationary to capture a shake-free image.
One solution is a “trial and error” approach where the photographer repeatedly captures and, using human effort, inspects the captured image for blur until a shake-free image is obtained. Another solution is for the photographer to only take photographs at “safe” exposures, refraining from taking a photograph whenever the exposure period is longer than the safe period. These solutions are less than satisfactory. The first approach adds to the time and effort needed to a capture a photograph. Additionally, capturing multiple images consumes battery power. Moreover, because of the need to capture multiple images, the photographer loses control over the timing of when an image is captured, which can result in lost photo opportunities. The second approach also results in forgone photo opportunities.
Accordingly, there is a need for methods and apparatus for efficiently detecting camera shake when capturing digital photographs.